Polymorphism and physiology of arsenate tolerance in Holcus lanatus L. from an uncontaminated site

The polymorphism of arsenate tolerance in a Holcus lanatus L. population from an uncontaminated soil was investigated and a high percentage of tolerant individuals (65%) was found in the population studied. Influx of arsenate was highly correlated to arsenate tolerance within the population, with the most tolerant individuals having the lowest rates of arsenate influx. Isotherms for the high affinity arsenate uptake systems were determined in six tolerant and six non-tolerant genotypes. Tolerant plants had the lowest rates of arsenate influx. This was achieved by adaptation of the V_max of arsenate influx with the V_max of the high affinity uptake system saturating at lower substrate concentrations in the tolerant plants. The polymorphism is discussed with relation to adaptation to the extreme environments to which the plants are subjected on mine-spoil soils.